If you have used Outlook 2003, 2007 or 2010 you might have noticed that every single email address you have typed in is stored and suggested next time you start typing the initial letters. This is a smart feature that saves allot of time.
However, some times you might want to remove and address or the whole cache.

To remove a single address, like if it is misspelled or something just simply press the delete button on the keyboard.

If you want to clear the whole cache do the following:

Outlook 2010
1) Quit Outlook
2) Press start and choose run
3) Type: Outlook.exe /CleanAutoCompleteCache and the press run
4) Close down Outlook again
5) Start Outlook and the cache should be empty

The Exchange Web Service (EWS) is the web service that allows access to the Out of Office service. If either the internal or external URL for the EWS is missing or incorrect, OOF will fail and other services may not work as expected.

Using Exchange Management Shell, check the URLs assigned to the web service virtual directory using the Get-WebServicesVirtualDirectory command. If either the internal or external URL is missing or incorrect, set them using the Set-WebServicesVirtualDirectory command.

Get-WebServicesVirtualDirectory

Type or paste this line into Exchange Management Shell to check the EWS URLs

Get-webservicesvirtualdirectory | fl identity,internalurl,externalurl

If the server is configured correctly, the command returns results similar to the following, with URLs in both the InternalUrl and ExternalUrl fields.